Male tubular elements of threaded connections are generally obtained by machining tubes which are tightened in jaws acting on the outer surface of the tubes.
For a variety of reasons, it may be necessary to machine the inner surface of the male tubular element close to the front surface of the free end.
As an example, for the efficiency of a metal-metal sealing surface close to a free end it is desirable to provide a defined constant thickness beneath the surface around the circumference.
Alternatively, when the front surface of the free end is to act as an axial abutment, the transverse cross section of that front surface must be well defined in order to determine the maximum makeup torque which that section can take.
Other circumstances can also arise.
The inner surface of the tubes carries imperfections, both macrogeometric (variations in diameter, eccentricity with respect to the outer surface) and microgeometric (surface quality).
API specification 5CT from the American Petroleum Institute (API) for casing and tubing prescribes the following tolerances:                for the external diameter, −0.50% to +1%;        for the thickness, ±12.5%;        for the mass, −3.5% to +6.5%.        
In respect of the internal diameter, the API indicates that the tolerances are governed by those for the external diameter and the mass. Thus, they are much wider than those for the external diameter.
Regarding the eccentricity of the internal surface with respect to the external surface, this is included in the tolerance for the thickness.
Conventionally, the internal surface is machined over an axial length of the order of 20 mm and this machined surface is connected to the internal surface of the remainder of the tube via a tapered chamfer with a small inclination: see, for example, the VAM ® catalogue published by the Applicant, under the NEW VAM® heading.
When the thickness of the tube is insufficient to allow effective machining of the internal surface, prior to machining, a reduction swaging of the end is performed (also known as tapering).
Such known measures may prove to be insufficient in some cases, for example when the sealing surface is not adjacent to the free end or in the immediate vicinity thereof or, and in particular, when the male element is a tubular element constituting a threaded connection intended to undergo diametrical expansion and to be sealed after expansion.
More particularly, we are concerned with threaded tubular connections intended to undergo diametrical expansion in the plastic deformation region using an expansion tool with a diameter that is greater than the internal diameter of the connection, which is axially displaced therein, as described, for example, in WO-A-02/01102.